It is known that foaming in the process liquid in a (gas-liquid separation) tower will substantially reduce the throughput capability thereof. Such foaming may result from the combined presence of a surface active process additive (or impurity) in the process liquid feed and the bubbling action of the process gas feed as it passes upwardly through the liquid moving over any of the plurality of separation (sieve) trays.
A method of foam inhibition in a static aqueous system is described in British Pat. No. 1,091,199. Therein, an antifoam composition reduced to a finely-divided state in a venturi is dispersed in a gas stream and this stream of gas containing the antifoam dispersion is continuously, or intermittently, introduced into a static aqueous medium. The British Patent teaches that the size of the droplets of antifoam composition is not critical provided they are sufficiently small to be carried into (i.e. they are not lost in transit) the foaming medium by the flow of gas. Without the exercise of control over the particle distribution size the range of particle size will typically extend from sub-micron size to 100 microns or more.
The problem faced in the control of foaming in industrial gas-liquid separation processes is unique in that the antifoaming composition may have to be delivered to trays hundreds of feet from the available sites for introduction of the antifoam composition to the separation tower.
In the conduct of studies attempting to solve the foaming problem in such gas-liquid separation towers, it has been determined that most antifoam agents lose their effectiveness after a fatigue time, which is usually of the order of 15-20 minutes or less. Since, in a separation tower about 300 feet high, the transit time for the process liquid is approximately one-half hour, an antifoam introduced into the process feed stream entering the top of the tower does not effectively reduce foaming on the lower trays. Moreover, since the transit time is long, it is not feasible to add the antifoam on an intermittent basis in response to foaming upsets. The consequent need for continued addition is economically unfavorable.
It would be particularly advantageous to be able to eliminate the need for continuous addition of antifoam composition.